1. Field of the Invention
The present invention relates to a process for preparing modified pigments comprising a pigment having attached at least one organic group, as well as to the resulting modified pigments. Inkjet ink compositions are also disclosed.
2. Description of the Related Art
The surface of pigments contain a variety of different functional groups, and the types of groups present depend on the specific class of pigment. Several methods have been developed for grafting materials to the surface of these pigments. For example, it has been shown that polymers can be attached to carbon blacks containing surface groups such as phenols and carboxyl groups. However, methods which rely on the inherent functionality of a pigment's surface cannot be applied generally because not all pigments have the same specific functional groups.
Methods for the preparation of modified pigment products have also been developed which can provide a pigment with a variety of different attached functional groups. For example, U.S. Pat. No. 5,851,280 discloses methods for the attachment of organic groups onto pigments including, for example, attachment via a diazonium reaction wherein the organic group is part of the diazonium salt. The resulting surface-modified pigments can be used in a variety of applications, such as inks, inkjet inks, coatings, toners, plastics, rubbers, and the like. Also, U.S. Pat. Nos. 6,328,894, 6,398,858, 6,214,100, and 6,221,142 describe modified pigments having attached organic groups, including groups comprising at least two carboxylic acid salt groups.
Other methods to prepare modified pigments have also been described. For example, PCT Publication No. WO 01/51566 discloses methods of making a modified pigment by reacting a first chemical group and a second chemical group to form a pigment having attached a third chemical group. Ink compositions containing these pigments are also described.
While these methods provide modified pigments having attached groups, there remains a need for improved processes for attaching groups and, in particular, organic groups comprising at least two carboxylic acid groups or salts thereof, to a pigment. These additional methods may provide advantageous alternatives to forming modified pigments as well as providing modified pigments with good overall performance in applications such as inkjet inks.